With more than 1.6 million Americans affected, inflammatory bowel disease (IBD) causes significant morbidity and can progress to colon cancer. There are two main forms of IBD: ulcerative colitis (UC) and Crohn's disease, and the associated abnormal immune response continues to be investigated with the goal of discovering new therapeutics or avenues for intervention. We have previously shown that in a prospectively collected cohort of adult UC patients, CCL11 (also called eotaxin-1), a chemoattractant for eosinophils, was the only analyte increased in both serum and tissue at all levels of disease severity out of 42 cytokines and chemokines assessed, compared to non-IBD control patients. We also observed a significant increase in colonic tissue eosinophils in UC patients vs. controls, and eosinophil counts correlated with tissue CCL11 levels. It has been shown that Ccl11-deficient mice were protected from colitis in an acute dextran sulfate sodium (DSS)-induced colitis model. However, acute colitis studies in mice lacking eosinophils have been mixed, suggesting it is not clearly just decreased tissue eosinophil infiltration leading to improvement. We have now determined that 1) Ccl11 mRNA is expressed in isolated colonic epithelial cells and isolated lamina propria cells in response to the chronic DSS and the azoxymethane (AOM)-DSS colitis-associated carcinogenesis (CAC) models; 2) epithelial cells and macrophages express receptors for CCL11; 3) treatment with an anti-CCL11 antibody leads to protection in an injury and repair model of colitis; 4) Ccl11?/? mice exhibit decreased tumor number, tumor burden, and colonic eosinophils in the AOM-DSS model; 5) bone marrow transplant studies point to loss of both hematopoietic and epithelial-derived CCL11 as key mediators of the protection seen in the AOM-DSS model; 6) CCL11 expression is increased in Apc mutant mouse tumors; and 7) the fecal microbiome is altered in Ccl11?/? mice compared to wild-type mice at baseline. In this proposal, we will dissect the role of CCL11 in modulating epithelial injury and repair, and immune responses in models of chronic colitis, CAC, and sporadic/genetically-mediated colon cancer. Our Hypothesis is: CCL11 is a key mediator of colonic inflammation, epithelial dysfunction, and risk for carcinogenesis. The overarching goal is to establish new insights into the potential benefits of blocking CCL11 signaling in both the treatment of colitis and prevention of colon carcinogenesis. The Specific Aims are: 1. To determine the mechanism of protection in colitis-associated cancer with loss of CCL11. Ccl11?/? mice exhibit protection in the AOM- DSS model associated with altered tissue cytokine levels and decreased tissue eosinophils. However, acute colitis studies in eosinophil-deficient mice suggest this may be an eosinophil independent effect. WT, Ccl11fl/fl, Ccl11?mye, Ccl11?GIepi, and Ccl11?/? mice exposed to AOM-DSS will be used to test the hypothesis that protective effects are due to altered immune cell populations other than eosinophils and/or epithelial function when CCL11 is lost by assessing tumor number and size, colonic immune cell composition/function, and epithelial function. 2. To determine if CCL11 is also a modifier in sporadic/genetically-mediated colon tumorigenesis. Loss of CCL11 protects from CAC in murine modeling, and CCL11 expression is increased in Apc mutant tumors. CDX2P-CreERT2Apcfl/fl and CDX2P-CreERT2Apcfl/flCcl11?/? mice that develop colon tumors will be used to test the hypothesis that loss of CCL11 will abrogate tumor development by reducing tumor- promoting inflammation by assessing: tumor number and size, colonic immune cell composition/function, and epithelial function. 3. To determine if targeting CCL11 signaling with neutralizing antibodies protects from colon tumorigenesis. WT mice exposed to AOM-DSS and CDX2P-CreERT2Apcfl/fl mice will be treated with a CCL11 neutralizing antibody (or isotype control) to establish the effects on: tumor number and size, colonic immune cell composition/function, and epithelial function. These studies will provide new mechanistic insights to support the use of treatments based on inhibition of CCL11 in colitis and colon cancer.